Wikipedia:Reference desk/Archives/Science/2006 October 27

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1 October 27

[edit] October 27

[edit] Where to Purchase Digestive Enzymes

I would appreciate if anyone would know where I could purchase these digestive enzymes:

Papain (Papaya), Bromelain (Pineapple), Ficin (Figs) and Actinidin (Kiwi). I am looking for a tablet or powdered form that is mostly the enzyme and tthe concentration for each enzyme is about the same, for comparison.

The problem I am finding is that the Health Stores only carry Papain and Bromelain and some of the biochemical companies sell only industrial size.

Would any universities carry them?

Thank you.

JDC

What country are you in? Are you at school? When i worked in a school lab we used to get most of our enzymes from normal school suppliers. SigmaAldrich carry pretty much everything but they will not sell to the public :-( Theresa Knott | Taste the Korn 00:14, 27 October 2006 (UTC)

The obvious question is: Why not eat the actual fruit to get all the good stuff, instead of hoping that whatever powder they give you actually contains what they claim ? StuRat 03:29, 27 October 2006 (UTC)

Well, Bromelain is easy, as is papain, as you say. You can get ficin here (about a hundred bucks for 25g), among other places; not sure where you can get pure actinidin in small quantities, but there's a commercial preparation of it called Zylax being sold over the net. --jpgordon^∇∆∇∆ 17:22, 28 October 2006 (UTC)

[edit] Pectodictyon

What is this genus (of algae, apparently), and why aren't any descriptions of it available online? Neon Merlin 02:17, 27 October 2006 (UTC)

Well, it's a genus within the family Hydrodictyaceae. – Clockwork Soul 04:46, 27 October 2006 (UTC)

[edit] Airships

I was reading the article on airships and finally made it to the artile discussing Orbital or high altitude airships. I was wondering if it is possible for a ballon or airship design to exist in a vacuum, wouldn't it explode? Also I read about JP areospace I think they have the right idea if it's possible but the ion drive is a bit farout. Is it possible with an airship in airless space to be driven with a rocket?67.126.141.80 04:44, 27 October 2006 (UTC)

An airship in a vacuum wouldn't explode (unless it was already close to exploding in air), but it wouldn't provide any lifting power. It would fall like a rock. How do you think a balloon works? Here's the relevant part from the first paragraph of the Airship article: ...primarily by means of a cavity (usually quite large) filled with a gas of lesser density than the surrounding atmosphere. If there is no surrounding atmosphere, it can't possibly work. —Keenan Pepper 05:02, 27 October 2006 (UTC)

A balloon can certainly exist in a vacuum: for example, the Echo satellites were balloons. It simply has to be constructed of a material that can withstand the temperatures it will encounter, which are likely to vary more in outer space than in the atmosphere. It's true that the same amount of gas inside will exert a stronger pressure on the balloon when it's in vacuum, and that could make it explode, but the simple solution to this is to use a smaller amount of gas inside.

Yes, you could drive a balloon in space by attaching it to a rocket, or to an ion drive. But it would not be functioning as an airship, because an airship floats in the air and in space it would not be floating on anything. On the other hand, if it was in orbit, it wouldn't need to.

--Anonymous, 05:05 UTC, October 27.

What? How could it possibly float if there is no air around it. No air is less dense than anything. --liquidGhoul 05:11, 27 October 2006 (UTC)

That's what I said, it would NOT be floating. --Anon, 22:43.

An airship in a vacuum would feel a greater amount of pressure on it than in an atmosphere, but good design will keep that under control. Bigelow Aerospace has successfully deployed some prototypes in orbit of inflatable modules (ultimately) designed for use in human-habitable stations, so it's quite doable. As to whether or not it would still qualify as an airship, that's a question of semantics, but it wouldn't get any sort of power from its internal gas - it would have to use a rocket or some traditional means of space propulsion to move. Virogtheconq 06:37, 27 October 2006 (UTC)

See Echo satellite for an article about early communication satellites which were giant balloons in space. Edison 12:27, 27 October 2006 (UTC)

[edit] composite materials

I need to do a Chemistry report and presentation. Hence, I need info about the meaning of composite materials, examples and components of composite materials, comparing and contrasting properties of composite materials, and justifying the properties of composite materials. If the information is received earlier, it would be better. Thank you. --61.6.47.6 06:24, 27 October 2006 (UTC)

Have you tried looking at composite material? It has everything you need right there. Virogtheconq 06:31, 27 October 2006 (UTC)

[edit] Sexual Dysfunction

Is there a cure for sexual dysfunction? How to solve premature ejaculation in males? What are the long term side effects of it? The male patient is 23 yrs old and has symptoms of the above? How long does one generally manintain his virginity? How does one define a virgin? Advise...

Although we are lucky enough to have several medical professionals who post to the boards, we discourage questions that require medical speculation or advice. After you read premature ejaculation, you might want to have 'the patient' contact a medical professional. Anchoress 09:08, 27 October 2006 (UTC)

How long can one maintain his sex drive? Till what age particularly the males?

See also Virgin, Sexual dysfunction, and Sex drive. Many people, male and female, retain a certain libido through old age, although typically diminished compared to when they were teenagers. --Lambiam ^Talk 10:51, 27 October 2006 (UTC)

There's a saying about male potency: 20 years old, triweekly. 50 years old, try weekly. 70 years old, try weakly. Edison 12:30, 27 October 2006 (UTC)

On loveline Dr. Drew sometimes talks about this premature ejaculation medicine that is in the works... something like an extremely short acting prozac. Xcfrommars 20:24, 27 October 2006 (UTC)

What is the age generally males have sex? Particularly in the west ?

Do you mean the first time they have sex? And what do you mean by "sex" - intercourse, masturbation, fellatio ... JackofOz 11:22, 30 October 2006 (UTC)

[edit] Communication Engineering

What is the difference between noise and distortion in communication?

Have you looked at our articles Noise and Distortion? In general, noise is a disturbance that is added to the signal, like hiss on an old grammophone record. Distortion can be any change in the signal shape, such as when a sound is muffled (high-frequency cut-off) or you turn up an amplifier too much. --Lambiam ^Talk 10:29, 27 October 2006 (UTC)

Simply put, distortion means a bad signal, while noise means no signal (or a random signal if you wish). Turn on the tv and take out the cable. The 'snow' you see is noise. DirkvdM 11:29, 27 October 2006 (UTC)

Ignore the above; it is noise. Actually "noise" can be used with two meanings: (1) additive disturbances, typically undesirable because they interfere with a proper transmission of the signal; (2) the same for a "zero" signal, so all that is left is "pure" noise. --Lambiam ^Talk 14:29, 27 October 2006 (UTC)

Electrical noise can be defined as an unwanted signal which is always present in a communication system. its presence tends to impede the reception of the wanted signal and is usually the limiting factor in its detection.

from Noise, F.R Connor, Pub. Edward Arnold 1973. ISBN 0 7131 3306 6. Chapter 1 para 1 --Light current 19:10, 27 October 2006 (UTC)

Noise is added to the signal from an external source, distortion is a modification of the signal through a non-linear function. --OpusPenguin 03:57, 28 October 2006 (UTC)

Yeah thats a nice defn, and one that I agree with apart from the fact that noise can be generated in the Rx. But do we have a valid source for that statement?--Light current 04:01, 28 October 2006 (UTC)

Hey, don't ignore me. Let me make some more noise. :)

Noise is 1) a random signal that 2) is unrelated to the intended signal. Or, as the noise article puts it, "an unwanted by-product of other activities". It also mentions the tv noise, but another good example is film grain. And I like the ad example, although that is not really random, just unrelated. I'm not as sure about the meaning of distortion, but I think noise is just one possible form of distortion. The distortion article, however, seems to contradict this. DirkvdM 09:38, 28 October 2006 (UTC)

Yes but an unwanted by product can also be distortion components. So the page is not accurate.--Light current 13:06, 28 October 2006 (UTC)

[edit] high frequency gravitational waves truth or myth

I have read about high frequency gravitational waves that should in theory have a number of effects such as propulsion and peterbation of objects, I have found a few webpages that deal with the subject that seem legitimate http://www.iop.org/EJ/abstract/0264-9381/22/10/046 http://www.iop.org/EJ/article/0264-9381/22/10/046/cqg5_10_046.pdf This one is from an institute used to study gravitational waves called LIGO http://www.ligo.caltech.edu/docs/G/G030067-00/G030067-00.ppt So are these waves a myth, a theory or can we just not make them yet? Rupert

Have you looked at Gravitational wave? In theory, whenever you wiggle your nose, it will generate gravitational radiation. However, despite strenuous efforts, scientists have not yet directly observed gravitational waves, not even from binary systems with black holes or neutron stars, much less from anything we can do. --Lambiam ^Talk 10:22, 27 October 2006 (UTC)

First of all, any gravitational wave would have the effects you mention, although the higher the frequency the more noticable the effect. As Lambian mentions the logistics of us creating them prevent us. It is almost certain that they do exist, but due to the weakenss of gravity they are very hard to detect. I can't remember how LIGO looked for them, but any terrestrial attempts are futile as the effect is almost certain to be lost amongst the vibrations of the planet. There is a mission planned that will use (I think) three satellites in orbit around the Sun with lasers pointing between them. If any gravitational waves move between them they should cause a blueshift in the lasers which could be detected. I hope I've been of some help.

All attempts at detection as far as I know are based on laser interferometry. The the satellite system, LISA looks promising. X [Mac Davis] (SUPERDESK|Help me improve) 04:31, 28 October 2006 (UTC)

[edit] Colour of dreams

A question that always evokes an interesting response, if not an intelligent answer, from people that I ask :) Do you dream in colour, or monochrome? Sandman30s 14:22, 27 October 2006 (UTC)

Colour. --liquidGhoul 14:27, 27 October 2006 (UTC)

Usually colours that are as vivid or more than in reality. Sometimes I have image-less dreams, or with dim and mute, almost monochromatic colours. --Lambiam ^Talk 14:34, 27 October 2006 (UTC)

Colour. Although I read somewhere that we all dream in colour, some people are just not capable of remembering in colour. :-)) Or they were trained to believe from a young age that some (or all) people dream in b/w, and that's what they've programmed themselves to remember. Anchoress 14:41, 27 October 2006 (UTC)

Generally I dream in colour, besides the odd exception. I've had a couple of grayscale dreams, or dreams which I remember being as such, but they were in the dark where I'd expect to see little if any colour in real life. I've also had a couple extremely abstract dreams that seemed to be purely black/white (ie. white letters on a black background, nothing else). There was also one which wasn't in grayscale but was all in shades of purple. -- Consumed Crustacean (talk) 15:37, 27 October 2006 (UTC)

Canadians dream in colour, Americans in color! This was the gist of my 1 min research on this issue: Recent experimental dream studies by Kahn et al. (11) have suggested that most, if not all, dreams are experienced in color, but that memory traces of the color perceptions are "bleached" progressively after awakening through various psychic mechanisms which are as yet unclear. --Zeizmic 15:44, 27 October 2006 (UTC)

And English people. This faq has always puzzled me. Why shouldn't people dream in colour if they see in colour? What would surely be remarkable is dreaming in shades of grey (or sepia, or anything else).--Shantavira 17:21, 27 October 2006 (UTC)

Places, people, situations and words are first remembered in dreams ; colors less, smells lesser (personal research). -- DLL ^{.. T} 17:48, 27 October 2006 (UTC)

I remember seeing stuff, feeling buoyancy, the touch of the ground, and the wind, but I can't remember if what I saw was in colour or black-and-white. --Kjoonlee 18:41, 27 October 2006 (UTC)

Can't remember if what I heard was in stereo either. :( --Kjoonlee 18:42, 27 October 2006 (UTC)

Color. Black Carrot 20:35, 27 October 2006 (UTC)

Many people remember a time when most TV was watched in black and white, either because it was broadcast that way or because color TV sets were too expensive. Go back just a few more years and most movies were black and white as well. I suggest that if people ever did commonly dream in black and white, the reason is very likely that they were conditioned by these media to form images that way. Remember, dreams are largely based on real experiences, and those could include watching TV or movies. --Anonymous, 22:55 UTC, October 27.

I have never dreamed in black and white, although many times I lose one or more of the senses. X [Mac Davis] (SUPERDESK|Help me improve) 04:28, 28 October 2006 (UTC)

My mother said that the night after we had bought a colour tv, she dreamt in colour for the first time. Probably a better way to put that is to say that she dreamt about colour. Whether I dream in colour, I haven't a clue. I've never noticed or paid attention to it and considering that my normal vision is in colour, I would probably have noticed if any dream were not in colour, so I suppose they are. DirkvdM 09:47, 28 October 2006 (UTC)

Like I said, interesting :) Some people go almost into a daydream state, racking their mind for what their dreams look like. I like the dim and mute and sepia etc. descriptions. Usually means your dream is hazy because the conscious mind can't tap into the subconscious at will. When anything colourful becomes hazy, colours merge or blend into something not quite monochromatic but close. You should never dream in black and white btw unless you live in a b&w world. The media conditioning answer is convincing, but surely your dream will at some point include the tv's colourful surroundings? Sandman30s 11:48, 30 October 2006 (UTC)

[edit] Earthing/Grounding

What are the merits and demerits of using rod earthing or plate earthing in household electricity?Which one is better?amrahs 17:30, 27 October 2006 (UTC)

I'd imagine a plate would be significantly more expensive to install and may have initial settling issues but would have a much lower resistance to the general mass off earth due to its much larger contact area. Plugwash 17:41, 27 October 2006 (UTC)

If you're building a new house, I'd recommend you install a Ufer ground instead of a rod or plate ground. Ufer ground example. 192.168.1.1 11:50, 27 Rocktober 2006 (PST)

I believe this is only necessary if you are building something totally isolated from a town water system, like a farmhouse or a cottage. --Zeizmic 19:57, 27 October 2006 (UTC)

The main purposes of grounding are: lightning protection, and protection against downed high-voltage power lines. A good ground will provide a high-current path which keeps the occupants of the house from becoming part of the electric circuit. Ground is only used as part of energy transmission system if you're out in the wilderness and using a [SWER|single-wire earth return] power line, and in that case the Utility company provides the grounding equipment. --Wjbeaty 02:20, 28 October 2006 (UTC)

""If requesting electrical wiring advice, please consider asking an electrical contractor or electrical engineer instead. That said, follow your local electrical code. Electricity is totally unforgiving of naivete or misunderstandings. Do not improvise methods based on "common sense." A short rod you stick in the ground by hand is about useless, as would be a small plate. In my part of the U.S. in normal soil conditions ground rods are generally used. Stainless steel rods are driven into rhe ground in about four foot sections. The first one has a sharp point. The following ones screw onto the first one. A driving cap is screwed onto the back while an electric or pneumatic driver drives it down. Sometimes 10 feet suffice, sometimes 30 feet is needed. The ground resistance is tested until it is down to the required level. Multiple rods a certain number of feet apart may be combined to lower the total resistance. Water pipes are not always sufficient, especially if there may be plastic anywhere in the system coming to the house. Allowable ground resistence depends on the available fault current and codes. If rock is hit, retry a few feet away or get a drilling rig. A plate system would have to be somehow deep enough to avoid damage from gardening etc and deep enough to stay moist, since ground resistance would increase in dry soil. The area where the plate system is would have to be marked or fenced off so no one ever damages it, as by trenching. It would somehow have to allow drainage. This plates might corrode away in a few years. The ground resistance of a deep rod is related to a hemispheric shell model. A plane would seem to lack the same area as a rod, at first blush, so you would have to excavate a large area. A commercial radio tower may have a series of radial cables buried to establish a ground . A substation in addition to a system of ground rods, may have a network of cables below the gravel to limit step and touch potentials in the event of a fault. In mountainous country, they have to improvise, such as grounds in springs or wells. Edison 16:28, 28 October 2006 (UTC)

[edit] measurement by vernier

how to use vernier caliper?

Go to vernier caliper and you can see one being used to measure a coin. --Kainaw ^(talk) 18:06, 27 October 2006 (UTC)

You probably mean Vernier scale. Vernier caliper redirects to caliper. BTW do you agree that it should rather redirect to Vernier scale? — Sebastian (talk) 22:09, 27 October 2006 (UTC)

I tried this instead of a redirect; what do you think? ike9898 03:55, 28 October 2006 (UTC)

If it is a vernier caliper, it is pretty easy. Just sandwich the movable tooth and fixed as close to the object as possilbe and read the ruler. I don't have one with me, and haven't used a caliper for a few months—reading it might be harder than that. X [Mac Davis] (SUPERDESK|Help me improve) 04:27, 28 October 2006 (UTC)

[edit] Tooth Transplant

Is it possible to get such a thing as a tooth transplant? Would I be able to get it done on the (UK) NHS as I am 17 and suffer from enamel hypoplasia.

Yours, Christopher

Assuming it was technically feasible (which I doubt), then, If you needed more than one tooth replacing, there would be a practical problem of getting a matching set to fit, unless they were all taken from a corpse with the same size mouth as yours. However, implants I believe are possible at about £2000 per tooth. 8-).--Light current 19:27, 27 October 2006 (UTC)

I'm no orthodontist, but wouldn't it be possible for the you to get a fake tooth implant instead of the real deal? If you haven't finished puberty you're probably close, so there would be no issue with the rest of the mouth outgrowing the fake tooth. (OK actually that last part makes little sense but my suggestion stands.) Hyenaste ^(tell) 19:58, 27 October 2006 (UTC)

About now as far as I know it is impossible to get real, living teeth transplanted. However, among other things, the future looks good for growing teeth. Turner's hypoplasia only affects one tooth, is this the case with you? Don't worry though, you can definitely get new teeth. My dad's teeth were pretty bad looking before he got some operations in Thailand. X [Mac Davis] (SUPERDESK|Help me improve) 04:24, 28 October 2006 (UTC)

Research is working on finding ways of transplanting or creating real teeth in place of missing ones, but at the moment implants are the closest things we have. - Dozenist talk 15:49, 28 October 2006 (UTC)

[edit] Walls

Do walls really need mortar? If so, why?--Light current 19:23, 27 October 2006 (UTC)

Walls don't need mortar, bricks do. But only if you want them to hold together. --BluePlatypus 19:25, 27 October 2006 (UTC)

OK do bricks/stones need mortar to make a wall and why?--Light current 19:28, 27 October 2006 (UTC)

So seagulls can't easily knock down the wall. --Zeizmic 19:50, 27 October 2006 (UTC)

Well if you have superglue, then you can use that to hold the bricks together. Otherwise, the bricks will just fall down every time there's a windstorm. --Bowlhover 19:59, 27 October 2006 (UTC)

Not true! Dry stone walls can last in wild windswept areas for centuries!--Light current 20:44, 27 October 2006 (UTC)

It all depends how massive the bricks/blocks/stones are. Plenty of walls, barns, and pyramids are built without mortar. Many single-skin walls built with mortar are actually quite easy to push over.--Shantavira 20:13, 27 October 2006 (UTC)

Mortar is just one of many ways to get blocks of stone or brick to stay together. Other methods include having overlapping pieces (like Legos) or just relying on mass and geometry to hold them together (as in Egyptian pyramids). Mortar seems to have a disadvantage that it doesn't last as long as the bricks or stones, so can shorten the life of a wall, relative to one held together by some other method. Mortar-free walls may also benefit from being able to expand and contract with changing temperatures, without building up stresses which result in cracks. Of course, anything connected to such walls also needs to be free to move, or the cracks will occur there. StuRat 20:38, 27 October 2006 (UTC)

Quite. It's certainly possible to do construction without mortar. Often such work demands much more skill from the craftsman, however. Each stone has to be carved to match the stone below. The aqueduct of Segovia is a Roman aqueduct built entirely without mortar that is nearly two thousand years old. TenOfAllTrades(talk) 20:49, 27 October 2006 (UTC)

So why do we actually use mortar in all modern masonry buildings?--Light current 20:53, 27 October 2006 (UTC)

Mass production concerns. It takes too long to assemble a wall from pieces that must be fit together like a puzzle - it's far cheaper and faster to manufacture bricks or quarry rocks and slap them together with some mortar.

Yeah but whats the mortar for???--Light current 21:48, 27 October 2006 (UTC)

It functions as an adhesive. AFAIK, the mortar penetrates the pores in bricks/rough surface on rocks before it cures, basically forming a bridge between otherwise separate pieces. 192.91.147.34 22:00, 27 October 2006 (UTC)

If it acts as an adhesive, what is its tensile strength? Concrete seems to have the lowest tenslie strength of any construction material [[1]] --Light current 23:41, 27 October 2006 (UTC)

No, not just that. Economical concerns. You need a thicker wall, using more work and more material, to build a wall that doesn't need mortar. Also, it's almost impossible to make the wall wind-proof. Why would you spend more money on a worse wall? Just because something is possible doesn't make it economical or practical. Note, by the way, that just about nothing at all is built out of stone blocks today, even with mortar. When stone is used, it's just a facade to make things look nice. In the 19th century you'd have a stone or plaster facade with bricks beneath, but today even that is too exensive. Today it'd be a wall of girders and cinder-blocks or a concrete beneath. --BluePlatypus 21:45, 27 October 2006 (UTC)

It's ironic. In the middle ages they plastered bricks to make a smooth surface and today we hide the smooth surface of concrete with bricks. DirkvdM 10:07, 28 October 2006 (UTC)

Hence faster and cheaper. 192.91.147.34 22:00, 27 October 2006 (UTC)

Windproofing is easily provided by outside render or inside plaster. Why must stone walls fit together like a puzzle?--Light current 21:47, 27 October 2006 (UTC)

A really rough explanation would be that without good contact on all surfaces (fitting together like a puzzle), there's not enough static friction to maintain the stability of the wall. There are also practical engineering concerns relative to proper transmission of forces on the wall to the places most able to handle the stress. 192.91.147.34 22:02, 27 October 2006 (UTC)

I have seen it said that mortar isn't there so much to hold the bricks together as to hold them apart. That is, the important thing is that it adjusts its shape (before it dries) to the exact shape of each brick, so they fit together better than if they were just stacked, and then the weight of the bricks works to hold the wall together. Of course this is an exaggeration; the mortar does contribute some adhesive power as well. But not a lot -- which is why masonry construction is not recommended in earthquake zones. It doesn't have a lot of tensile strength, so the walls are subsceptible to being shaken apart. --Anonymous, 23:00 UTC, October 27.

I think Anonymous has provided the most satisfying (to me) answer yet. It makes perfect sense! Spreading the load seems very important. I wonder how many bricklayers know the answer?--Light current 23:52, 27 October 2006 (UTC)

For a house, you can't underestimate the importance of a weather shield from acid rain. The inside would accumulate water and cause mold (without a sealant, such as mortar). High-rises use a granite face, but each segment is sealed with silicone. You could put silicone as a mortar, but that's expensive, and only done for glass bricks. As well, in some circumstances, a well-mortared brick wall has considerable resistance to in-plane shear during an earthquake. --Zeizmic 01:46, 28 October 2006 (UTC)

Did I not already say that an external render could keep out the rain?--Light current 18:59, 28 October 2006 (UTC)

Wouldn't construction be a lot easier and faster if bricks had a standardised profile such that they would interlock, so you could just stack them? Sort of like Lego. Anyone can build a wall with that. No need to apply mortar or wait for it to dry. Possibly with a thin layer of plastic on the brick's surface to add friction and make a wall wind proof, although I doubt that would be necessary. Actually, doesn't something like that already exist? DirkvdM 10:07, 28 October 2006 (UTC)

That's a good question, and deserves it's own posting:

[edit] Why aren't large interlocking bricks practical for construction ?

(See discussion above.) StuRat 15:59, 28 October 2006 (UTC)

A Lego style brick wall, like the stone blocks fitted together by the Incas, is just the sort of thing used for retaining walls. The cast blocks interlock, and are used to cover an exposed dirt bank, like next to a sidewalk where the lawn is elevated a few feet. But they are not even close to waterproof. Water drains easily through the interfaces between the bricks. A tightly stacked brick wall would do the same, unless a rubber gasket, expanding foam or some such was installed between the bricks as a seal. The dimensional stability of such a gasketed wall would be questionable, since the gasket would compress over time. Cathedrals and castles were usually been built of large stone blocks without mortar. The stones have to be precisely shaped, or carved to match the irregularities of the one below as in Inca construction. The thickness of the stone blocks is great enougn to lessen the wind blowing through and moisture migration. Brick walls usually are far less thich, with a saving of materials. For stone blocks of jails, splines like cannonballs were sometimes placed in carved recesses in the stones between courses to make sure a stone could never be moved relative to its neighbors. Mortar acts as an adhesive to enhance the integrity of the wall and help prevent it being pushed over by external forces, but an old wall will often stay intact "by force of habit" even if the bricks are no longer stuck adhesively together.. The mortar is waterproof, or at least water resistant when new. A driven rain would come right through a stacked brick wall, so you could not have wood, plaster or drywall as an inside wall covering. If you had a stone or brick floor, the water would trickle down the wall and go away eventually. The mortar is softer than the brick, by design. The proportion of Portland cement in the mortar must not be too high, so that as the wall settles and moves tiny distances in settling, the mortar gives rather than the brick. After several decades, enough mortar will have washed away that Tuckpointing [2] is needed, in which some crumbly mortar is chisled or ground away and fresh mortar troweled into the gap. A "struck joint" is done when the brick wall is first made, by using a pointing trowel to compress the mortar into the joint 1/4 inch or so. "Buttering the joint" is a poor tuckpointing practice of just filling in that gap with more mortar, which degrades the appearance of the wall.Edison 16:57, 28 October 2006 (UTC)

I don't know what sort of limit you've applied to "large," but I've built a couple retaining walls before using interlocking bricks (I don't recall the exact size, but it was somewhere around half a cubic foot) without mortar. My guess for larger projects is again economics: concrete is cheaper for large projects, since once a form is built (which isn't a lot of effort, depending on the shape) it really just needs to be poured, whereas the effort for bricks scales pretty much linearly with size. However, since the inital effort for concrete forming/pouring is somewhat time-intensive, I'm guessing for smaller projects brickwork is a tad more efficient (and more stylish in today's culture). There's also something to be said for the portability of concrete in a slushy form, compared to the ginormous rigid volume occupied by a massive brick. Virogtheconq 17:02, 28 October 2006 (UTC)

I said lego, but I meant something more like a profile, so that at any point the water would have to go up, which it won't if it's rain). The tight fit of the incas and the mediaeval churches was a lot of work, but with today's technology, surely we can make bricks that are exact copies of each other (within a very small tolerance, I mean). If such bricks are thus tightly packed, the joins would be no less watertight than the brick itself (unless they are coated, when they would be even more watertight). Btw, I didn't mean large bricks. They could be the same size as standard bricks. The advantage is that anyone can build such a wall, at a speed of just a few seconds per brick. A 3x3 m wall contains about 500 bricks and would take about half an hour to build. Now that's fast, and with the high cost of labour that would mean a huge saving, especially if you don't need to hire a professional. DirkvdM 08:50, 29 October 2006 (UTC)

In a region with freezing and thawing, water between the brick courses would expand when it froze, de-stabilizing the structure. Mortar could keep the moisture out. Edison 22:59, 29 October 2006 (UTC)

Bricks are somewhat porous, so don't they have the same problem (internally)? Anyway, my assumption was that we could make bricks with very narrow tolerance margins, so any water seeping through (if any, given the surface tension of water) would only form a flimsy layer. Also, a wall made of loose bricks might be more flexible, although I'm not sure if that doesn't contradict the aforementioned assumption. DirkvdM 10:36, 30 October 2006 (UTC)

[edit] Colon Cancer

I've got a vegetarian here trying to convince me that red meat can lead to colon cancer. This I've confirmed (at least, I've confirmed there exist doctors who believe it) online, but he further claims that it's caused by a buildup of actual undigested red meat in the person's colon, and that the average middle-aged (presumably American, since that's where we are) male has "several pounds of undigested red meat" in their colon. Should I be buying this? Black Carrot 19:30, 27 October 2006 (UTC)

According to Meat consumption and risk of colorectal cancer: A meta-analysis of prospective studies there is an association between red meat eating and increased risk of colon cancer. Eating 120 g/day of red meat was associated with an approximately 20-40% increased risk. --JWSchmidt 20:09, 27 October 2006 (UTC)

Yes, there is a risk, but no, that's not the reason. I've heard that said before, though, by some nutrition nut on TV, perhaps Gary Null. However, I do understand that a lack of fiber in the diet can leave some partially digested food stuck to the sides of the intestinal wall. I doubt if it's "several pounds", and this would include various foods, not just red meat. A healthy diet will include lots of fiber and minimize the consumption of meat (red and otherwise), as such meat is high in bad fats and bad cholesterol. Fish and vegetable fats and cholesterol are actually good for you, though, so eat plenty of those (like olive oil and avocados). StuRat 20:25, 27 October 2006 (UTC)

If anyone tells you your bowels are lined with undigested food, please label all past and future health and science advice from that person as absolutely worthless. Surgeons look at bowels every day. All it takes to clean you completely out is one bottle of mag sulfate. The bowels are so cleaned out you can shine a light through the walls. The obsession with whether your bowels are really moving everything through is classic American folk medicine, like the French with their livers and the Malaysians with koro. alteripse 21:30, 27 October 2006 (UTC)

Trying giving up all meat for a week or two, then see how you feel. If your guts feel cleaner, if you have more energy, if your bowel movements are easier, it might be something worth keeping up over the long run. Nevermind what doctors, scientists, and vegetarian health nuts have to say. -- Chris 23:36, 27 October 2006 (UTC)

Yeah, doctors and scientists have no idea what they're talking about. I can be serious though in saying "vegetarian health nuts have no idea what they are talking about." "Several pounds" sounds like another "figure not looked up, but made up"—have you ever seen the inside of a sigmoid colon? It isn't that big. Grab a several-pound ham and decide if you could fit it in there. Another activity would be to ask him what kind of undigested material would be in his colon if he ate several pounds of corn—if we're talking about food items that are not digested very well, then vegetable products and rocks are probably top on the list. X [Mac Davis] (SUPERDESK|Help me improve) 04:19, 28 October 2006 (UTC)

You could easily fit several pounds of meat into the sigmoid - it's able to distend to an amazing degree. However, as has been stated, anyone who is familiar with colonoscopy can tell you that pounds of meat are not in the average colon. I mean, thousands of colonoscopies are done every day in which the colonic walls are directly visualized and meat is not found. InvictaHOG 15:20, 28 October 2006 (UTC)

BTW, the question just stated "colon" (the entire large intestine), so why are we restricting the answer to the sigmoid colon only ? StuRat 15:55, 28 October 2006 (UTC)

I feel that the phrase "vegetarian health nut" is perjorative, and has no place on this reference desk. We vegetarians think very carefully about what we eat, and our longevity proves that we have some sensible ideas. --G N Frykman 08:42, 28 October 2006 (UTC)

I suppose it depends on the interpretation. If taken to mean "all vegetarians are nuts", then I agree. If taken to mean "this person is a nut, and also happens to be a vegetarian", then that's not so bad. StuRat 15:40, 28 October 2006 (UTC)

Well, looking back over the comments, it seems to take three forms - The first was the original comment about the guy on TV, who might well have been a nut, the second was a later comment about "scientists, doctors, and vegetarian health nuts", which looks like it was meant to be more playful than anything else, and the third was Mac Davis commenting on the shameful prevalence of urban legends in our society. Not that it much matters, but since you brought up the question, I figured I'd mention that the answer is right there. Regarding my friend, he's not really a health nut. And I'm not yet convinced he's wrong. The restriction of the answer to the "sigmoid colon", which I've just discovered is a rather small chamber right at the end of the real colon, seems a bit odd. Or is that a normal way of referring to it? Looking a the picture, I could actually imagine quite a bit of stuff gunking up the large intestine itself, without preventing flow entirely, especially having been forced to sit through all those videos of gunked-up heart tubes. Perhaps even several pounds of stuff, though I'm not good at estimating weight. Also, [3] (the pictures, not the article) seems to suggest that there really is a surprising amount just sitting there being gross, though I'm not sure that's a reliable source of info. So, I'd like to restate my question slightly. 1) Given the entirety of the large intestine, how much non-useful (since I realize some slime is good for you) gunk does a normal person have, 2) How much is made up of undigested food, 3) Which foods would contribute to that (we currently have corn and meat as potential contributors), 4) Does it impair functioning, 5) If it isn't a buildup of rotting food that does it, how does meat contribute to cancer, and 6) How did you arrive at your answer? I eagerly await your further replies. Black Carrot 18:45, 28 October 2006 (UTC)

How much clearer can we make it? There is no build-up. Every day, thousands of surgeons and gastroenterologists look directly at, through, and in people's colons. There is no "build-up" that is sitting there without moving through each day as you defecate. All it takes to make you clean from one end to the other is a single dose of a cathartic, the same way people are prepared for surgery or colonoscopy. And we are not just talking about the sigmoid colon, but the entire small and large intestines. Anyone who tells you otherwise is full of crap (paradoxically, so to speak). The second issue, which is whether meat-based diets incur a higher risk of colon cancer, is an entirely separate issue that does not involve visible "build-up" anywhere. Anywhere. alteripse 04:00, 29 October 2006 (UTC)

It's not clear how meat causes cancer. Here is one article on it: [4]. Another possibility is simple replacement. That is, people who eat large quantities of meat tend to eat fewer fruits, vegetables, whole grains, etc., and thus miss out on the cancer protection effects of those foods. StuRat 03:36, 29 October 2006 (UTC)

Re the replacement theory, that wouldn't mean that meat causes cancer, would it. It would be the absence of other necessary dietary ingredients that's the problem, not the presence of meat per se. No? JackofOz 09:10, 31 October 2006 (UTC)

[edit] the word for when stuff feels nice

hello, hope you can help, its driving me mad. what is the word for the study of when tangible objects feel nice. not in a dodgy wierdo way, but when car doors clunk well, switches switch securely, and hand tool type things are nice and heavy. my computer mouse feels plastic and rubbish; my new bottle opener is made of some grippy metal feels sort of well balanced. its not ergonomics, but is something like that............ please, thankyou, lovely people, etc simon

That was the word I was going to use. It's also "farfignuten" in German and "consay engineering" in Japanese (I have no clue how either is spelled). BTW, this question belongs on the Language Ref Desk. StuRat 20:28, 27 October 2006 (UTC)

You mean Kansei Engineering?

Yes, that it. I've never seen it in print before now. StuRat 23:38, 27 October 2006 (UTC)

Is it just me, or does that article not say anything concrete? It is as if our article on Mezcal would go like: "Mezcal is a potion that can make people happy. Since it was introduced, the world has become a better place." --Lambiam ^Talk 00:38, 28 October 2006 (UTC)

Yeah, that article is a little weak. ike9898 04:41, 28 October 2006 (UTC)

Well engineered. Neat! Nice! 8-)--Light current 20:48, 27 October 2006 (UTC)

Solid, smooth, cool 8-)--Light current 21:44, 27 October 2006 (UTC)

Tactile? Clarityfiend 21:45, 27 October 2006 (UTC)

Did you check the article on "haptic"? — Sebastian (talk) 21:55, 27 October 2006 (UTC)

Or for that matter, the synonym of septic? X [Mac Davis] (SUPERDESK|Help me improve) 04:11, 28 October 2006 (UTC)

Sometimes, I've heard the things you mentioned described as being satisfying. ike9898 04:39, 28 October 2006 (UTC)

I know the feeling. The word 'snug' also comes to mind. Something that fits snugly in your hand or a (backpack) buckle that clicks without the need to use much force, but doesn't rattle either, meaning it's a perfect fit. But 'heavy' is also an important word here. Like a Mac mouse. Or a door that refuses to slam, but instead makes a civilised 'clonk' sound, the way doors of heavy expensive cars do. You don't need to close it explicitly, just give it a push (momentum) and it continues on its way and when it closes encounters the 'padding' of first the lock and then the weather strip - neither too hard nor too soft. Just 'snug'. But that's too general a word. 'Solid' also comes close, but both words are too general. DirkvdM 12:04, 28 October 2006 (UTC)

"Phat" or "Da bomb." Edison 17:00, 28 October 2006 (UTC)

So that's why some people call their girlfriends "phat"? --Wirbelwindヴィルヴェルヴィント (talk) 17:24, 28 October 2006 (UTC)

That stands for "Pretty, Hot, And Tempting". StuRat 07:56, 29 October 2006 (UTC)

[edit] dynamic motion

A girl running at a constant speed of 2.3 m/s in a straight line throws a ball directly upward at 4.4 m/s. How far will she travel before the ball drops back into her hands? Ignore air friction.—Preceding unsigned comment added by 24.99.59.96 (talk • contribs)

Do your own homework. If there's a specific concept you need help grasping, we can aid you. We won't your homework questions for you, though. -- Consumed Crustacean (talk) 20:49, 27 October 2006 (UTC)

Word. Since it probably won't occur to you to politely rephrase the question in a more general form, or better yet, since it's a fairly standard physics problem, search for it yourself, here's where you can find the answer: Equations_for_a_falling_body. Black Carrot 21:10, 27 October 2006 (UTC)

How long does it take for the ball to accelerate from 4.4 m/s, to 0, and to 4.4 m/s again? And how far can the girl run in that period of time? --Bowlhover 22:27, 27 October 2006 (UTC)

In US English, that's "How long does it take for the ball to decelerate from 4.4 m/s, to 0, and accelerate back to 4.4 m/s again ?". Note that the girl's motion does not matter, since the ball takes on the exact same motion. StuRat 23:06, 27 October 2006 (UTC)

I don't think it's a US v british thing, it's a science v common usage thing. The scientific defination of acceleration is "change in velocity" speeding up, slowing down, changing direction are all accelerations. Theresa Knott | Taste the Korn 23:12, 27 October 2006 (UTC)

Yes, but it's customary in the US to refer to negative accel as decel. It sounds as strange to us to say "accelerate down to zero" as it would be for you to say "heat the solution down to absolute zero" or "pay the customer -$15". StuRat 23:26, 27 October 2006 (UTC)

Acceleration/deceleration in whose frame of reference? Granted this is a more simple situation, but there are many cases where an object will be appearing to slow down from one person's viewpoint, yet speed up from another person's viewpoint. Acceleration in a scientific context, like, say, you might find on a science reference desk, is merely the rate of change of momentum with respect to time, a vector quantity. For a fixed-mass object, it's the rate of change of velocity w.r.t. time, also a vector - with magnitude and direction, where direction is often denoted by a + or -. In this situation (due to approximation for this type of science question), the acceleration is a constant, the ball is accelerating downwards due to a constant force - gravity. Note that in forming the equations of motion, you do not have to treat the slowing down to zero speed and speeding back up to 4.4 m/s as separate parts of the trajectory. Richard B 00:33, 28 October 2006 (UTC)

StuRat, the question asks "how far will she travel before the ball drops back into her hands". So the girl's motion does matter. --Bowlhover 23:30, 27 October 2006 (UTC)

I should clarify my statement. The girl's motion does not matter in determining how long it will be until she will catch the ball. However, her motion does matter in determining the distance she will travel in that time. StuRat 06:17, 28 October 2006 (UTC)

Air resistance (plus a small gust of wind) will cause the ball to lose forward speed and clunk her on the head. Then she will run home and do her own homework. Edison 17:05, 28 October 2006 (UTC)

Wow, you sure told him. Good thing he didn't say "ignore air friction", or you'd look a little silly. Black Carrot 18:20, 28 October 2006 (UTC)

Do your own homework.But I will give the concepts

Consider the Initial Upward Velocity of the ball as b
We know that v=u+at . And re arranging you get t=(v-u)/a In this case, v=0 and a=-g and u=b
So time needed for the ball to come to rest when thrown upward is t=(0-b)/-g=b/g
So time needed for the ball to come again to the ground is time=2b/g
Time is 2*4.4/9.8
The horizontal velocity of the girl is 2.3
Velocity = Displacement/Time
Displacement = Velocity x Time
Distance covered = Displacement = 2.3 x 2 x 4.4 / 9.8 = 2 metres

I have not checked whether the ball will fall to the ground or fall in her hands.

For that you need to use a formula involving tangential values. I joined in Medical College 10 years ago. Since then I have not used these formulas. Hence I am not able to recollect the second formula that is also used to calculate the range of artillery fire, military tanks etc. ANy doubts, please leave a message in my talk page Doctor Bruno 20:21, 28 October 2006 (UTC)

[edit] Title of doctor.

Are the following people allowed to use the title of doctor in the United Kingdom?

Dentists (with the degree BDS) Chiropractors (with the degree MChiro) Nurses (whith say Ph.Ds but practice as nurses) Podiatrists (with Bachelors degrees)

Thank you

Dentists are doctors but their titles are 'Mister' (meaning surgeon).
I dont think you'ld get many PhDs acting as nurses!
I dont think podiatrists are classed as medical doctors.
Opticians are doctors
Chiropractors --- Im not sure, probably not

--Light current 22:35, 27 October 2006 (UTC)

The dentist one puzzled me as my first dentist called himself Mr but my next one and the whole surgery went by Doctor. So, like medical doctors with MCh degrees who call themselves Mister, they ARE entitled to use Doctor?
Well, I know this is fictional, but there was a nurse in ER who had a Ph.D. I wasnt sure where this matter stood
thank you
There are 2 new Chiropractors in town with BSc and MChiro degrees and go by "Practice Doctors" and have doctor in front of their name.

Christopher

Yes all surgeons in UK whether dental or otherwise call themselves 'Mister' (a throwback to the days when barbers used to do it).--Light current 22:45, 27 October 2006 (UTC)

That comment about nurses is pretty derogatory. Nursing is a tough profession and I'm sure I could find you handfuls of nurses with phds. Aaadddaaammm 02:42, 28 October 2006 (UTC)

I dont think you'ld get many PhDs acting as nurses! How is that derogatory?--Light current 03:02, 28 October 2006 (UTC)

A search for "nurse phd" gives 3,850,000 pages [5] through google. Many different programs are evidently available to gain a phd in nursing. Aaadddaaammm 03:59, 28 October 2006 (UTC)

So?--Light current 04:28, 28 October 2006 (UTC)

Opticians are doctors in the UK? In the U.S., Opthalmologists are MDs and optometrists have Doctor of Optometry degrees but opticians are technicians which may not even have a university degree. --OpusPenguin 03:12, 28 October 2006 (UTC)

Yes I believe so.--Light current 03:28, 28 October 2006 (UTC)

Anyone can use the title "Doctor" in the UK, it is not illegal to adopt that title. As has been mentioned many times on this 'desk, most British medical practitioners are not "real doctors" in the historical sense of the word, as they do not have a doctorate (like an MD). Most are Bachelors of Medicine and call themselves doctor by convention only. Its a self-imposed, honourific title that is now synonymous with their profession, but historically it means something very different. Same goes for dentists and podiatrists. Ironically enough, in your example, the only "real" doctors are the nurses with PhDs.

In the UK its only illegal to use the title to defraud, so you can go around calling yourself "Doctor Light current" if you wish, as long as in doing so, you do not try to use the title to imply you offer medical skills, services or authority. The only people that can use the title "Doctor" to offer medical services are those registered with the GMC or equivilant. Rockpocket 06:39, 28 October 2006 (UTC)

Well anyone with a PhD calls themselves Doctor in the UK. And medical doctors, who dont, do!--Light current 13:34, 28 October 2006 (UTC)

True, but only "medical doctors" are registered with the General Medical Council, hence their real title is a "registered medical practitioner". The only real "medical doctors" are those with an MD or a PhD and MB BChir/MB BCh/MB ChB/BM BS/MB BS et al. Rockpocket 18:30, 28 October 2006 (UTC)

So going by the MBBS article, it appears that UK medical doctors can start practicing medicine five or six years out from high school, is that right? Whereas in the States you need a four-year undergrad degree, four-year MD, plus a residency. Presumably we pay for all that extra education in our medical bills. Not that I personally am in any position to complain about that :-) I'm just wondering whether we get anything for it. Are our doctors smarter than UK ones? Better able to diagnose and treat unusual complaints? Has any objective comparison been made of the standard of care? --Trovatore 18:47, 28 October 2006 (UTC)

Actually I think its 7 yrs total un UK : 3 yrs medicine + surgery, then 4 yrs on the job to get the other qual. I think in the UK we get our Masters Degrees in these extra 4 yrs, but I could be wrong. Therefore

Are our (US) doctors smarter than UK ones? --

A.No.

But a masters degree does not entitle one to call oneself Doctor (as in Ph.D)

--Light current 20:29, 28 October 2006 (UTC)

Its an interesting question. I happen to work in bio-medicine and interact with med students and youngish doctors from both countries. While its not a case of one being smarter than the other, in my experience, there certainly is a difference. Firstly, in general, US medics tend to be better educated (because they have a wider tertiary education) and thus appear more learned. They also tend to be more "focussed", for want of a better word. This is because many decide to become a medic when they are older and thus more mature and also because the cost of completing an MD is the US is astronomical compared to the UK. Its not all pro-US though, the motivation of the UK medics tend to be more Hippocratic. I detect a financial motivation much more in the US students (though i suspect that is both a cultural thing and also because the financial outlay is so great.)

That said, however, this is based on observing the individuals during their training process. Inevitably, the cream rises and chaff is separated during their training, and, when you compare the fully trained medical professionals, i don't really think there is a major difference. Even if there is, its hard to control for the difference in medical systems between the two countries. If you took the British medical community and gave them the resources the private sector afford the US community, who is to say what the standard of care would be? Similarly for US doctors working within the NHS. Rockpocket 20:49, 28 October 2006 (UTC)

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